The present invention relates to acrolein-releasing emulsion homopolymers, the process for producing them, and their use as biocides.
It is known that monomeric acrolein (2-propenal) is a very effective biocide for use in treating waterways to suppress undesired algal and plant growth. It can also be used against sulfate-reducing bacteria in petroleum exploration.
Other areas of application for the biocidal action of monomeric acrolein have not yet appeared because of its high reactivity. For instance, studies have shown that acrolein is subject to rapid alterations in aqueous systems, such as hydration or polymerization, depending on the pH (see FIG. 1). For that reason it has not been possible in the past to use acrolein as a preservative with long-lasting action. Because of its tendency to polymerize spontaneously, and sometimes explosively, with unexpert handling, it can be handled only by utilizing special safety procedures. It has a strong irritating action on the respiratory organs and the eyes. Acrolein has only limited storability even in the stabilized form.
It is known that copolymers of acrolein and formaldehyde can be made through condensation of acrolein and formaldehyde at molar ratios from 1:1 to 1:10 in the presence of a basic catalyst, and that they can be used as biocides for aqueous systems (German Patent Application B 32 05 484). The known copolymers of acrolein with formaldehyde have the disadvantage that they contain about 15% free unreacted formaldehyde.
Acrolein homopolymers are also known for use as biocides (European Patent Application 0 339 044). The polymerization is done predominantly by a free-radical process. The resulting polyaldehyde structures produced are supposed to be the carriers of the biocidal action. It is a disadvantage of the acrolein homopolymers produced by the free-radical process that they are not soluble in organic media or in water. Moreover, in the form of an aqueous suspension, they have only a very low biological activity.
The production of polyacroleins described in German Patent Application P 44 04 404 is problematic, because the yields from the reaction of acrolein with NaOH in an aqueous system are only 75-80% polymeric material. Therefore the mother liquor and wash water contain organic materials and must be disposed of at high cost. Recycling is impossible because of its bad effect on the polymer properties. These polymers, too, are nearly insoluble in water.
Acrolein polymers or copolymers which serve as sources of acrolein have not previously been described. The monomeric acrolein which is released continuously at low concentrations under suitable conditions should be a biocidal agent which is produced over a long period from the polymer or copolymer.
Emulsion polymers of acrolein have themselves been known for a very long time. H. Cherdon et al. describe production of emulsion polymers of acrolein using polyacrolein-SO.sub.2 - solutions as the emulsifier (in Makromolekulare Chem. 32, 197 (1959)).
Margel and Wiesel published the production of analogous products with defined particle sizes in, among other places, the Journal of Polymer Science, Polymer Chemistry Edition, Vol. 22, 145 (1984), and in U.S. Pat. No. 4,783,336. The polymerization is carried out under alkaline conditions with sodium hydroxide, or free radical polymerization with persulfate/silver as the catalyst. Use as a marker for cell determinations or in transmission electron microscopy is also mentioned.
European Patent Application 0 441 468 A2 describes the use of microparticles based on polyaldehydes, for example, as contrast agents.
Therefore an object of the invention is to provide an effective biocide agent for use in many applications which avoids prior art problems dealing with acrolein.
A further object of the invention is to produce acrolein homopolymers which have good biocidal activity and which can be handled simply.